More than 2000 years ago Hippocrates (460-377 BCE) said, "If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health." What does that mean when it comes to water? Water has been described as a neglected, unappreciated, and under-researched subject, and further complicating the issue, a lot of the papers extolling the need for proper hydration are funded by the bottled water industry.

It turns out the often quoted "drink at least eight glasses of water a day" dictum has little underpinning scientific evidence . Where did that idea come from? The recommendation was traced to a 1921 paper, in which the author measured his own pee and sweat and determined we lose about 3% of our body weight in water a day, or about 8 cups (see How Many Glasses of Water Should We Drink in a Day?). Consequently, for the longest time, water requirement guidelines for humanity were based on just one person.

There is evidence that not drinking enough may be associated with falls and fractures, heat stroke, heart disease, lung disorders, kidney disease, kidney stones, bladder and colon cancer, urinary tract infections, constipation, dry mouth, cavities, decreased immune function and cataract formation. The problem with many of these studies is that low water intake is associated with several unhealthy behaviors, such as low fruit and vegetable intake, more fast-food, less shopping at farmers markets. And who drinks lots of water? People who exercise a lot. No wonder they tend to have lower disease rates!

Only large and expensive randomized trials could settle these questions definitively. Given that water cannot be patented, such trials seem unlikely; who's going to pay for them? We're left with studies that find an association between disease and low water intake. But are people sick because they drink less, or are they drinking less because they're sick? There have been a few large prospective studies in which fluid intake is measured before disease develops. For example, a Harvard study of 48,000 men found that the risk of bladder cancer decreased by 7% for every extra daily cup of fluid we drink. Therefore, a high intake of water--like 8 cups a day--may reduce the risk of bladder cancer by about 50%, potentially saving thousands of lives.

The accompanying editorial commented that strategies to prevent the most prevalent cancers in the West are remarkably straightforward in principle. To prevent lung cancer, quit smoking; to prevent breast cancer, maintain your ideal body weight and exercise; and to prevent skin cancer, stay out of the sun. Now comes this seemingly simple way to reduce the risk of bladder cancer: drink more fluids.

Probably the best evidence we have for a cut off of water intake comes from the Adventist Health Study, in which 20,000 men and women were studied. About one-half were vegetarian, so they were also getting extra water by eating more fruits and vegetables. Those drinking 5 or more glasses of water a day had about half the risk of dying from heart disease compared to those who drank 2 or fewer glasses a day. Like the Harvard study, this protection was found after controlling for other factors such as diet and exercise. These data suggest that it was the water itself that was decreasing risk, perhaps by lowering blood viscosity (blood thickness).

Based on all the best evidence to date, authorities from Europe, the U.S. Institute of Medicine, and the World Health Organization recommend between 2.0 and 2.7 liters (8 to 11 cups) of water a day for women, and 2.5 to 3.7 liters (10 to 15 cups) a day for men. This includes water from all sources, not just beverages. We get about a liter from food and the water our body makes. So this translates into a recommendation for women to drink 4 to 7 cups of water a day and men 6 to 11 cups, assuming only moderate physical activity at moderate ambient temperatures.

We can also get water from all the other drinks we consume, including caffeinated drinks, with the exception of stronger alcoholic drinks like wines and spirits. Beer can leave you with more water than you started with, but wine actively dehydrates you. However, in the cancer and heart disease studies I mentioned above, the benefits were only found with increased water consumption, not other beverages.

Surprised that the 8-a-day rested on such flimsy evidence? Unfortunately, so much of what we do in medicine has shaky underpinnings. That's the impetus behind the idea of evidence-based medicine (what a concept!). Ironically, this new movement may itself undermine some of the most effective treatments. See Evidence-Based Medicine or Evidence-Biased?

What kind of water? I recommend tap water, which tends to be preferable from a chemical and microbial contamination standpoint. What about buying one of those fancy alkalizing machines? See Alkaline Water: a Scam?

More than 2000 years ago Hippocrates (460-377 BCE) said, "If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health." What does that mean when it comes to water? Water has been described as a neglected, unappreciated, and under-researched subject, and further complicating the issue, a lot of the papers extolling the need for proper hydration are funded by the bottled water industry.

It turns out the often quoted "drink at least eight glasses of water a day" dictum has little underpinning scientific evidence . Where did that idea come from? The recommendation was traced to a 1921 paper, in which the author measured his own pee and sweat and determined we lose about 3% of our body weight in water a day, or about 8 cups (see How Many Glasses of Water Should We Drink in a Day?). Consequently, for the longest time, water requirement guidelines for humanity were based on just one person.

There is evidence that not drinking enough may be associated with falls and fractures, heat stroke, heart disease, lung disorders, kidney disease, kidney stones, bladder and colon cancer, urinary tract infections, constipation, dry mouth, cavities, decreased immune function and cataract formation. The problem with many of these studies is that low water intake is associated with several unhealthy behaviors, such as low fruit and vegetable intake, more fast-food, less shopping at farmers markets. And who drinks lots of water? People who exercise a lot. No wonder they tend to have lower disease rates!

Only large and expensive randomized trials could settle these questions definitively. Given that water cannot be patented, such trials seem unlikely; who's going to pay for them? We're left with studies that find an association between disease and low water intake. But are people sick because they drink less, or are they drinking less because they're sick? There have been a few large prospective studies in which fluid intake is measured before disease develops. For example, a Harvard study of 48,000 men found that the risk of bladder cancer decreased by 7% for every extra daily cup of fluid we drink. Therefore, a high intake of water--like 8 cups a day--may reduce the risk of bladder cancer by about 50%, potentially saving thousands of lives.

The accompanying editorial commented that strategies to prevent the most prevalent cancers in the West are remarkably straightforward in principle. To prevent lung cancer, quit smoking; to prevent breast cancer, maintain your ideal body weight and exercise; and to prevent skin cancer, stay out of the sun. Now comes this seemingly simple way to reduce the risk of bladder cancer: drink more fluids.

Probably the best evidence we have for a cut off of water intake comes from the Adventist Health Study, in which 20,000 men and women were studied. About one-half were vegetarian, so they were also getting extra water by eating more fruits and vegetables. Those drinking 5 or more glasses of water a day had about half the risk of dying from heart disease compared to those who drank 2 or fewer glasses a day. Like the Harvard study, this protection was found after controlling for other factors such as diet and exercise. These data suggest that it was the water itself that was decreasing risk, perhaps by lowering blood viscosity (blood thickness).

Based on all the best evidence to date, authorities from Europe, the U.S. Institute of Medicine, and the World Health Organization recommend between 2.0 and 2.7 liters (8 to 11 cups) of water a day for women, and 2.5 to 3.7 liters (10 to 15 cups) a day for men. This includes water from all sources, not just beverages. We get about a liter from food and the water our body makes. So this translates into a recommendation for women to drink 4 to 7 cups of water a day and men 6 to 11 cups, assuming only moderate physical activity at moderate ambient temperatures.

We can also get water from all the other drinks we consume, including caffeinated drinks, with the exception of stronger alcoholic drinks like wines and spirits. Beer can leave you with more water than you started with, but wine actively dehydrates you. However, in the cancer and heart disease studies I mentioned above, the benefits were only found with increased water consumption, not other beverages.

Surprised that the 8-a-day rested on such flimsy evidence? Unfortunately, so much of what we do in medicine has shaky underpinnings. That's the impetus behind the idea of evidence-based medicine (what a concept!). Ironically, this new movement may itself undermine some of the most effective treatments. See Evidence-Based Medicine or Evidence-Biased?

What kind of water? I recommend tap water, which tends to be preferable from a chemical and microbial contamination standpoint. What about buying one of those fancy alkalizing machines? See Alkaline Water: a Scam?

As you can see in my video, Plant-Based Diets and Diabetes, we've known for decades that a plant-based diet may be protective against diabetes. Studies going back half a century found that those eating meat one or more days a week had significantly higher rates of diabetes, and the more frequently meat was eaten, the more frequent the disease. And this is after controlling for weight, so even at the same weight, those eating more plant-based had but a fraction of the diabetes rates. If anything, vegetarians should have had more diabetes just because they appear to live so much longer, so they had more time to develop these kinds of chronic diseases; but no, apparently lower rates of death and disease.

Fast forward 50 years to the Adventist-2 study, looking at 89,000 people, and we see a stepwise drop in the rates of diabetes as one eats more and more plant-based, down to a 78% lower prevalence among those eating strictly plant-based. Protection building incrementally as one moved from eating meat daily, to eating meat weekly, to just fish, to no meat, and then to no eggs and dairy either. Followed over time, vegetarian diets were associated with a substantially lower incidence of diabetes, indicating the potential of these diets to stem the current diabetes epidemic.

We see the same step-wise drop in rates of another leading killer, high blood pressure. The greater the proportion of plant foods, the lower the rates of hypertension, and the same with excess body fat. The only dietary group not on average overweight were those eating diets composed exclusively of plant foods, but again there was the same incremental drop with fewer and fewer animal products. This suggests that it's not black and white, not all or nothing, any steps we can make along this spectrum of eating healthier may accrue significant benefits.

What about eating a really healthy diet with just a little meat? Is it better to eat none at all? We have new insight last year from Taiwan. Asian diets in general tend to be lower in meat and higher in plant foods compared with Western diet, but whether a diet completely avoiding meat and fish would further extend the protective effect of a plant-based diet wasn't known, until now.

Traditionally, Asian populations have had low rates of diabetes, but a diabetes epidemic has since emerged, and appears to coincide with increased meat, animal protein, and animal fat consumption, but the Westernization of Asian diets also brought along a lot of fast food and junk, and so these researchers at the national university didn't want to just compare those eating vegetarian to typical meateaters. So, they compared Bhuddist vegetarians to Bhuddist non-vegetarians, eating traditional Asian diets. Even the omnivores were eating a predominantly plant-based diet, consuming little meat and fish, with the women eating the equivalent of about a single serving a week, and men eating a serving every few days. That's just 8% of the meat intake in the U.S., 3% for the women. The question: is it better to eat 3% or 0%?

Again, both groups were eating healthy; zero soda consumption, for example, in any group. Despite the similarities in their diet, and after controlling for weight, family history, exercise, and smoking, the men eating vegetarian had just half the rates of diabetes, and the vegetarian women just a quarter of the rates. So even in a population consuming a really plant-based diet with little meat and fish, true vegetarians who completely avoided animal flesh, while eating more healthy plant foods, have lower odds for prediabetes and diabetes after accounting for other risk factors. They wanted to break it up into vegan versus ovo-lacto like in the Adventist-2 study, but they couldn't because there were no cases at all of diabetes found within the vegan group.

The reason I keep going back to that Adventist-2 study is that it's not only the biggest study of those eating plant based diets in North America, but the largest such study anywhere anytime. We owe those investigators a great debt (not to mention the 96,741 participants!). One thing I'm happy my tax dollars are going towards (via the National Cancer Institute and National Institutes of Health). More from the Adventists in Caloric Restriction vs. Animal Protein Restriction.

One of my favorite cancer-specific charities, the American Institute for Cancer Research, lauds the China Study and the documentary Forks Over Knives, with which they share the same bottom-line message: The healthiest diets are those that revolve around whole plant foods.

They then translate that advice into their Ten Recommendations for Cancer Prevention, featured in my video Which Dietary Factors Affect Breast Cancer Most? We now have evidence that those who follow such advice are actually protected against cancer. Breast cancer risk was reduced by 60% in women who met at least five recommendations compared with those who met none. The most important dietary advice was to be as lean as possible within the normal range of body weight, eat mostly foods of plant origin, and limit alcoholic drinks.

What about other cancers? Greater adherence to the AICR dietary guidelines was also associated with significantly less endometrial, colorectal, lung, kidney, stomach, oral, liver, and esophageal cancer. In other words, adherence to dietary recommendations for cancer prevention may lower the risk of developing most types of cancer. The drop in bladder cancer did not reach statistical significance, but a larger follow-up study following 469,000 people for 11 years (the largest to date) found that just a 3% increase in the consumption of animal protein calories was associated with a 15% higher risk of bladder cancer, whereas just a 2% increase in plant protein was associated with a 23% lower risk.

AICR recommendation number ten is that cancer survivors should follow the recommendations for cancer prevention. The same diet that can help prevent cancer in the first place can be used to help save our life after diagnosis. Adherence to the guidelines for cancer prevention was found to be associated with lower mortality among older female cancer survivors, or breast cancer and other cancers in general.

A cancer diagnosis is considered a teachable moment to get people eating and living healthier. Oncologists revel at the growth in the number of cancer survivors in this country, now ten million strong and growing. It's great that those with cancer are living longer, but even better to prevent it in the first place so we can all live longer. Not only does adherence to the guidelines lower cancer risk, but extends our lifespan because the guidelines are also significantly associated with a lower hazard of dying from heart disease and respiratory disease, suggesting that following the recommendations could "significantly increase longevity."

Just like eating to prevent cancer helps to prevent heart disease, eating to protect our heart helps prevent cancer. It sounds self-evident, but adherence to a healthy lifestyle is therefore associated with a lower risk of mortality overall. And the more healthy behaviors we have, the longer we get to live. Such factors included not smoking, walking every day, or eating green leafy vegetables almost daily.

To help differentiate the effects of diet from other lifestyle behaviors like smoking and drinking on cancer incidence, Adventists were recently compared to Baptists. Both discourage alcohol and tobacco, but the Adventists go further, encouraging a reduction of meat. In general, the Adventists had lower cancer hazard rates than the Baptists, and within Adventist populations, the vegetarians did even better, and those eating the most plants, did the best.

Why do plant-based diets appear to lower the risk of cancer? A number of fascinating mechanisms:

Every year I scour the world's scholarly literature on clinical nutrition, pulling together what I find to be the most interesting, practical, and groundbreaking science on how to best feed ourselves and our families. I start with the thousands of papers published annually on nutrition (27,000 this year--a new record!) and, thanks to a crack team of volunteers (and now staff!), I'm able to whittle those down (to a mere 8,000 this year). They are then downloaded, categorized, read, analyzed, and churned into the few hundred short videos. This allows me to post new videos and articles every day, year-round, to NutritionFacts.org. This certainly makes the site unique. There's no other science-based source for free daily updates on the latest discoveries in nutrition. The problem is that the amount of information can be overwhelming.

Currently I have more than a thousand videos covering 1,931 nutrition topics. Where do you even begin? Many have expressed their appreciation for the breadth of material, but asked that I try to distill it into a coherent summary of how best to use diet to prevent and treat chronic disease. I took this feedback to heart and in 2012 developed Uprooting the Leading Causes of Death, which explored the role diet may play in preventing, arresting, and even reversing our top 15 killers. Not only did it rise to become one of the Top 10 Most Popular Videos of 2012, it remains my single most viewed video to date, watched over a million times (NutritionFacts.org is now up to more than 1.5 million hits a month!).

Every year I wonder how I'm going to top the year before. Knowing how popular these live presentations can be and hearing all the stories from folks about what a powerful impact they can have on people's lives, I put my all into this new 2015 one. I spent more time putting together this presentation than any other in my life. It took me an entire month, and when you see it I think you'll appreciate why.

This year, I'm honored to bring you Food as Medicine, in which I go through our most dreaded diseases--but that's not even the best part! I'm really proud of what I put together for the ending. I spend the last 20 minutes or so (starting at 56:22) going through a thought experiment that I'm hoping everyone will find compelling. I think it may be my best presentation ever. You be the judge.

You can watch it at no cost online, but it is also available on DVD through my website or on Amazon. If you want to share copies with others, I have a five for $40 special (enter coupon code 5FOR40FAM). All proceeds from the sales of all my books, DVDs, downloads, and presentations go to the 501c3 nonprofit charity that keeps NutritionFacts.org free for all, for all time. If you want to support this initiative to educate millions about eradicating dietary diseases, please consider making a donation.

Many studies have shown that calorie restriction, without malnutrition, can increase lifespan and lower the risk of age-related diseases, such as cancer.

However, for many people, calorie restriction clearly has its drawbacks. In the classic Minnesota Starvation Study, many of the volunteers suffered a preoccupation with food, constant hunger, binge eating, and lots of emotional and psychological issues. Even researchers who study caloric restriction rarely practice it. There's got to be a better way to suppress the aging engine enzyme, TOR (see Why Do We Age?for more on TOR).

That's why researchers were so excited about rapamycin, a drug that inhibits TOR, thinking it could be caloric restriction in a pill. But like any drug, it a long list of potentially serious side effects. There's got to be a better way.

The breakthrough came when scientists discovered that the benefits of dietary restriction may be coming not from restricting calories, but from restricting protein intake (See my video Caloric Restriction vs. Animal Protein Restriction). If we look at the first comprehensive, comparative meta-analysis of dietary restriction, "the proportion of protein intake was more important for life extension than the degree of caloric restriction." In fact, just "reducing protein without any changes in calorie level have been shown to have similar effects as caloric restriction."

That's good news. Protein restriction is much less difficult to maintain than dietary restriction, and it may even be more powerful because it suppresses both TOR and IGF-1, the two pathways thought responsible for the dramatic longevity and health benefits of caloric restriction.

Some proteins are worse than others. One amino acid in particular, leucine, appears to exert the greatest effect on TOR. In fact, just cutting down on leucine may be nearly as effective as cutting down on all protein. Where is leucine found? Predominantly animal foods: eggs, dairy, and meat (including chicken and fish). Plant foods, such as fruits, vegetables, grains, and beans, have much less.

"In general, lower leucine levels are only reached by restriction of animal proteins." To reach the leucine intake provided by dairy or meat, we'd have to eat nine pounds of cabbage--about four big heads--or 100 apples. These calculations exemplify the extreme differences in leucine amounts provided by a conventional diet in comparison to a plant-based diet. The functional role of leucine in regulating TOR activity may help explain the extraordinary results reported in the Cornell-Oxford-China Study, "since quasi-vegan diets of modest protein content tend to be relatively low in leucine."

This may also help explain the longevity of populations like the Okinawa Japanese, who have about half our mortality rate. The traditional Okinawan diet is only about 10% protein, and practically no cholesterol, because they ate almost exclusively plants. Less than one percent of their diet was fish, meat, eggs, and dairy - the equivalent of one serving of meat a month and one egg every two months. Their longevity is surpassed only by vegetarian Adventists in California, who have perhaps the highest life expectancy of any formally studied population in history.

Dietary factors are considered the most important environmental risk factors for cancer. Within recent years, a large number of naturally occurring health-enhancing substances of plant origin known as phytonutrients have been recognized to have beneficial effects on certain cancers. Beans, chickpeas, split peas and lentils are packed with all sorts of wonderful nutrients, but the reason they may protect against several degenerative diseases may be due to non-nutritive compounds, or even so-called "antinutrient" compounds like phytates.

Phytates have a somewhat negative reputation for binding to certain minerals (like iron, zinc and manganese) and slowing their absorption. But they have also been found to offer anti-inflammatory health benefits. "The reputation of phytate has had a roller coaster ride ever since its discovery; it has undergone alternate eminence and infamy." (I previously explored the surprising new science about phytates in my video Phytates for the Prevention of Osteoporosis). Could they play a potential role in preventing colon cancer?

In the U.S., colon cancer is the second leading cause of cancer death, but some parts of the world have had just a tiny fraction of our rates, with the highest rates reported in Connecticut, and the lowest in Kampala, Uganda. The famous surgeon Denis Burkitt spent 24 years in Uganda and most of the hospitals he contacted there had never seen a case of colon cancer. Noting they live off diets centered on whole plant foods, he figured that maybe it was the fiber that was so protective.

Some studies have called that interpretation into question. Danes appear to have more colon cancer than Finns, yet Danes consume almost twice the dietary fiber. What else, then, could explain the low cancer rates among plant-based populations? Well, fiber isn't the only thing found in whole plant foods, but missing from processed and animal foods. Maybe it's the phytate.

Dietary phytate, rather than fiber per se, may be the most important variable governing the frequency of colon cancer, as phytate is known to be a powerful inhibitor of the iron-mediated production of hydroxyl radicals, a particularly dangerous type of free radical. So the standard American diet may be a double whammy, the heme iron in muscle meat plus the lack of phytate in refined plant foods to extinguish the iron radicals.

This may account for what researchers found in the Adventist study, highlighted in my video, Phytates for the Prevention of Cancer. They found excess risk of cancer for higher intakes of both red meat and white meat, suggesting all meats contribute to colon cancer formation -- about twice the risk for red meat eaters, and three times the risk for those eating chicken and fish.

Those who eat meat could reduce their risk in two ways: by cutting down on meat or by eating more beans, an excellent source of phytates.

So it's not just how much meat we eat, but our meat to vegetables ratio. Between the two extremes (high-vegetable and low-meat diets versus high-meat and low-vegetable diets) a risk ratio of about eight appears to exist, sufficient to explain a substantial part of the international variation in the incidence of colorectal cancer. Those with the worst of both worlds, high meat and low vegetable, were at eight times the risk.

Cervical cancer is now considered a sexually transmitted disease. It was originally suspected as such, but now we have DNA fingerprinting proof that virtually all cervical cancer is caused by a sexually transmitted virus, human papilloma virus, which also causes cancers of the penis, vagina, vulva and throat. HPV is considered a necessary, but not sufficient cause of cancer.

I profile a study in my four minute video, Why Might Vegetarians Have Less HPV?, that shows that while most young women contract HPV, most don’t get cervical cancer because their immune systems are able to clear out the virus. Within one year, 70 percent of women clear the infection, and more than 90 percent clear it within two years — before the virus can cause cancer.

Might those with particularly strong immune systems clear the virus even faster? That’s what may be behind a new study that found vegetarian women had significantly lower infection rates with HPV, one of many studies reporting lower risk of HPV infection among those eating plant-based diets.

When researchers took a bunch of women with cancer-causing strains of HPV infecting their cervix and followed them out and retested at three months and nine months while analyzing their diets, what did they find? Higher levels of vegetable consumption appeared to cut their risk of HPV persistence in half, doubling one’s likelihood of clearing this potentially cancer-causing infection. And “higher” levels just meant about two or more servings a day. Antioxidants appear to suppress the activation of critical segments of the virus’ DNA. Maybe that’s why smearing green tea on genital warts—also caused by HPV—has been found so effective in clearing them (See my video, Treating Genital Warts with Green Tea).

In terms of preventing cervical cancer, phytonutrients like lutein (found in dark green leafy vegetables) and lycopene (the red pigment in tomatoes) may decrease viral load, thereby decreasing persistence and progression to disease. Bottom line: higher consumption of vegetables may decrease the risk of HPV persistence, which may help explain why a 2013 study found vegan women have significantly lower rates of all female cancers combined, including cancer of the cervix.